This invention relates generally to roller bearings and more particularly to roller bearings for use in applications having movement over only a limited arc, as in the case of swashplates in variable-displacement axial piston pumps and motors.
Variable-displacement axial piston pumps and motors have rotating cylinder blocks and employ swashplates which tilt in an oscillating manner to control piston travel within the cylinders. In current heavy duty swash plate applications, because of their limited motion, the swashplates are commonly supported by roller bearing saddle segments. Since it is difficult to machine a semi-cylindrical surface with a high degree of accuracy, these bearing segments may be made as large pieces of bearing quality material with cylindrical bored, machined, and ground fully circular raceways which are then cut to the correct arc value. This method of fabrication results in discard of a portion of the costly machined and ground components of bearing quality material. Moreover, the bearing segments take up added space because of the thickness of components dictated by the fabrication method. Assembly into the machine is also made more difficult by the number of separate individual race, roller, cage, and timing components which must be installed.
In medium duty applications, the same handling of heavy parts, waste of expensive materials, and other fabrication difficulties exist, but for this less severe service, instead of roller bearings, bronze/polytetrafluorethylene sleeve liners are used in the interface between the bearing faces of the swashplate and the saddle. Although this substitution somewhat simplifies fabrication of the bearing, the performance of the assembly in service is often unreliable in that it is difficult to smoothly adjust displacement of the piston pump and/or motor due to intermittent sticking and slipping between the sleeve liners and the bearing faces. This stick-slip is the cause of jerky overcontrol of the machine which results in operator discomfort, erratic performance and even a safety hazard due to non-response or delayed-response to control movements.
The foregoing illustrates limitations known to exist in present swashplate bearings, and it would be advantageous to provide an alternative directed to overcoming one or more of those limitations. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.